U.S. patent number 6,108,513 [Application Number 09/289,378] was granted by the patent office on 2000-08-22 for double sided imaging.
This patent grant is currently assigned to Indigo N.V.. Invention is credited to Benzion Landa, Ishaiau Lior, Yossi Rosen, Boaz Tagansky.
United States Patent |
6,108,513 |
Landa , et al. |
August 22, 2000 |
Double sided imaging
Abstract
A system for double-sided imaging on a continuous-web substrate
having first and second substrate surfaces, the system including an
imaging device including a toner-image bearing surface having
selectively formed thereon first and second images. The system
further includes a web-feeder system which selectively brings the
first and second substrate surfaces into operative engagement with
the toner-image bearing surface, to transfer thereto the first and
second images, respectively, in accordance with a preselected
imaging sequence.
Inventors: |
Landa; Benzion (New Ziona,
IL), Lior; Ishaiau (New Ziona, IL), Rosen;
Yossi (Rehovot, IL), Tagansky; Boaz (Rishon
Lezion, IL) |
Assignee: |
Indigo N.V. (Maastricht,
NL)
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Family
ID: |
26323018 |
Appl.
No.: |
09/289,378 |
Filed: |
April 12, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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188208 |
Nov 9, 1998 |
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930249 |
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Foreign Application Priority Data
Current U.S.
Class: |
399/384; 399/309;
399/401 |
Current CPC
Class: |
G03G
15/232 (20130101); G03G 2215/00455 (20130101) |
Current International
Class: |
G03G
15/00 (20060101); G03G 15/23 (20060101); G03G
015/00 () |
Field of
Search: |
;399/384,385,401,302,308,309,364 ;101/179,220,229 ;271/184,225 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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9004216 |
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Apr 1990 |
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WO |
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9301531 |
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Jan 1993 |
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WO |
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9321566 |
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Oct 1993 |
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WO |
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9402887 |
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Mar 1994 |
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WO |
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9416364 |
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Jul 1994 |
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WO |
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9427193 |
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Nov 1994 |
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WO |
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9613761 |
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May 1996 |
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WO |
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Other References
IBM Disclosure Bulletin, vol. 22, No. 6, Nov. 1979, New York, pp.
2465-2566, K. Sanders, "Two-Path Electrophotographic Print
Process". .
Xerox Disclosure Journal, vol. 9, No. 3, May 1984, Stamford, CT,
pp. 201-203. Edward C. McIrvine "Method for Duplex Printing on
Continuous Web Paper"..
|
Primary Examiner: Chen; Sophia S.
Attorney, Agent or Firm: Greenblum & Berstein,
P.L.C.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation of application Ser. No.
09/188,208, filed Nov. 9, 1998, which is a continuation of
application Ser. No. 08/930,249, filed Jun. 6, 1995, now abandoned
which is the U.S. National Stage of International Application No.
PCT/NL95/00199, filed Jun. 6, 1995. The entire disclosure of
application Ser. Nos. 09/188,208 and 08/930,249 is considered as
being part of the disclosure of this application, and the entire
disclosure of application Ser. Nos. 09/188,208 and 08/930,249 is
expressly incorporated by reference herein in its entirety.
Claims
What is claimed is:
1. Image forming apparatus for double-sided imaging on a
continuous-web substrate, having first and second surfaces on
opposite sides of the substrate, comprising:
an imaging device comprising an image bearing surface moving in a
given direction and having selectively formed thereon first and
second images; and
a web-feeder system which selectively brings said first and second
substrate surfaces into operative engagement with said image
bearing surface, to transfer thereto said first and second images,
respectively, in accordance with a preselected imaging sequence,
wherein the first substrate surface engages the image bearing
surface at a first transfer region and the second substrate surface
engages the image bearing surface at a second transfer region, the
second transfer region being displaced from the first transfer
region in the given direction.
2. Apparatus according to claim 1 wherein the predetermined imaging
sequence comprises first surface imaging cycles, during which
cycles the first images are transferred to the first substrate
surface, and second surface imaging cycles, during which cycles the
second images are transferred to the second substrate surface.
3. Apparatus according to claim 2 wherein the predetermined imaging
sequence comprises a plurality of consecutive first surface imaging
cycles followed by alternating, first surface and second surface,
imaging cycles.
4. Apparatus according to claim 3 wherein the web-feeder system
comprises a first impression member which urges the continuous
substrate against the image bearing surface during each first
surface imaging cycle, and a second impression member which urges
the continuous substrate against the image bearing surface during
each second surface imaging cycle.
5. Apparatus according to claim 4 wherein the web-feeder system
further comprises a substrate inverter, operating on the continuous
substrate between said first and second impression members, which
inverts between the first and second surfaces of the continuous
substrate.
6. Apparatus according to claim 4 wherein the web-feeder system
comprises a substrate advance mechanism operative for advancing the
continuous substrate through said first and second transfer
regions.
7. Apparatus according to claim 6 wherein the web-feeder system
further comprises a controller which controls the advance of the
continuous substrate through the first and second transfer regions,
in accordance with the predetermined imaging sequence, by
controlling the operation of the substrate advance mechanism.
8. Apparatus according to claim 7 wherein the controller controls
the engagement and disengagement of said first and second substrate
surfaces with said image bearing surface, in accordance with the
predetermined imaging sequence, by controlling the position of the
first and second impression members relative to the image bearing
surface.
9. Apparatus according to claim 7 wherein the first images are
formed on the first substrate surface with a preselected
spacing.
10. Apparatus according to claim 9 wherein the imaging device
produces a post-image mark on the space following each first image
on the first substrate surface.
11. Apparatus according to claim 10 wherein the advancing mechanism
rewinds a preselected length of the continuous substrate through
the first transfer region following each first surface imaging
cycle.
12. Apparatus according to claim 11 wherein the continuous
substrate is accelerated to a surface velocity comparable with that
of the image bearing surface before each first surface imaging
cycle.
13. Apparatus according to claim 11 wherein the web-feeder system
further comprises a first mark detector associated with the first
substrate surface, ahead of the first transfer region, which
detects the post image marks on the first substrate surface and
produces first detection signals in response thereto.
14. Apparatus according to claim 13 wherein the controller triggers
each first surface imaging cycle in response to the first detection
signal of the preceding post-image mark.
15. Apparatus according claim 11 wherein the advance mechanism
rewinds a preselected length of the substrate through the second
transfer region following each second surface imaging cycle.
16. Apparatus according to claim 15 wherein the continuous
substrate is accelerated to a surface velocity comparable with that
of the image bearing surface before each second surface imaging
cycle.
17. Apparatus according to claim 16 wherein the web-feeder system
further comprises a second mark detector associated with the second
substrate surface, ahead of the second transfer region, which
detects the post image marks on the first substrate surface and
produces second detection signals in response thereto.
18. Apparatus according to claim 17 wherein the controller triggers
each second surface imaging cycle in response to the second
detection signal of the preceding post-image mark.
19. Apparatus according to claim 11 wherein the web-feeder system
further comprises a cutter, associated with the continuous
substrate downstream of the second transfer region, which cuts the
continuous substrate at the spaces between the first images on the
first substrate surface.
20. Apparatus according to claim 19 wherein the web-feeder system
further comprises a third mark detector associated with the first
substrate surface, ahead of the cutter, which detects the post
image marks on the first substrate surface and produces third
detection signals in response thereto.
21. Apparatus according to claim 20 wherein the controller
activates the cutter in response to the third detection
signals.
22. Apparatus according to claim 11 wherein the web-feeder system
further comprises at least one free-loop arrangement which contains
a variable length of the continuous substrate.
23. Apparatus according to claim 22 wherein the at least one
free-loop arrangement comprises a first free-loop arrangement ahead
of the first transfer region.
24. Apparatus according to claim 23 wherein the at least one
free-loop arrangement comprises a second free-loop arrangement
between the first transfer region and the second transfer
region.
25. Apparatus according to claim 24 wherein the web-feeder system
further comprises a third free-loop arrangement, between the second
transfer region and the cutter, which contains a variable length of
the continuous substrate.
26. Apparatus according to claim 11 wherein the web-feeder system
further comprises a first length detector, associated with the
continuous substrate between the first and second transfer regions,
which produces an electric output responsive to the position of the
continuous substrate relative to the first transfer region.
27. Apparatus according to claim 26 wherein the first length
detector comprises an encoder.
28. Apparatus according to claim 26 wherein the controller
addresses the first mark detector only within preset, first,
detection time windows and wherein the time gaps between the first
detection windows are set in accordance with the output of the
first length detector.
29. Apparatus according to claim 26 wherein the web-feeder system
further comprises a second length detector, associated with the
continuous substrate downstream of the second transfer region,
which produces an electric output responsive to the position of the
continuous substrate relative to second transfer region.
30. Apparatus according to claim 29 wherein the second length
detector comprises an encoder.
31. Apparatus according to claim 29 wherein the controller
addresses the second mark detector only within preset, second,
detection time windows and wherein the time gaps between the second
detection windows are set in accordance with the outputs of the
first and second length detectors.
32. Apparatus according to claim 29 wherein the controller
addresses the third mark detector only within preset, third,
detection time windows and wherein the time gaps between the third
detection windows are set in accordance with the output of the
second length detector.
33. Apparatus according to claim 1 wherein the image bearing
surface comprises a developed imaging surface.
34. Apparatus according to claim 33 wherein the imaging surface
comprises a photoreceptor surface.
35. Apparatus according to claim 1 wherein the imaging device
comprises an intermediate transfer member and wherein the image
bearing surface comprises a surface of the intermediate transfer
member.
36. Apparatus according to claim 1 wherein at least some of the
images comprise toner images.
37. A method for double-sided imaging on a continuous-web
substrate, having first and second surfaces on opposite sides of
the substrate, using an imaging device including an image bearing
surface, the method comprising:
providing a series of first images on said image bearing
surface;
transferring each image of the series of first images from the
image bearing surface to the first substrate surface;
providing a series of second images on said image bearing surface;
and
transferring each image of the series of second images from the
image bearing surface to the second substrate surface,
wherein none of the images in the series of first images are
transferred simultaneously with any of the images in the series of
second images and wherein providing said series of first images and
said series of second images comprises first, consecutively forming
a plurality of first images and, then, alternatingly forming first
and second images.
38. An imaging method according to claim 37 wherein transferring
each image of the series of first images comprises transferring the
images in the series of first images at a first transfer region and
wherein transferring each image of the series of second images
comprises transferring the images in the series of second images at
a second transfer region.
39. An imaging method according to claim 38 herein the image
bearing surface moves in a given direction and wherein the second
transfer region is displaced from the first transfer region in the
given direction.
40. An imaging method according to claim 38 and further comprising
inverting the first and second substrate surfaces of the continuous
substrate between the first and second transfer regions.
41. An imaging method according to claim 38, wherein said providing
a series of first images, said transferring each image of the
series of first images, said providing a series of second images
and said transferring each image of the series of second images are
performed in accordance with a predetermined image sequence and
further comprising advancing the continuous substrate through said
first and second transfer regions in accordance with said
predetermined imaging sequence.
42. An imaging method according to 38 wherein transferring each
images of the series of first images to the first substrate surface
comprises transferring the images with a preselected spacing.
43. An imaging method according to claim 42 and further comprising
producing a post-image mark on the space following each first
image.
44. An imaging method according to claim 43 and further comprising
rewinding a preselected length of the continuous substrate through
the first transfer region following transferring of each first
image.
45. An imaging method according to claim 44 and further comprising
accelerating the continuous substrate to a surface velocity
comparable with that of the image bearing surface before
transferring of each first image.
46. An imaging method according to claim 45 and further comprising
detecting the post image marks on the first substrate surface ahead
of the first transfer region.
47. An imaging method according to claim 46 and further comprising
triggering a transferring of each first image in response to a
post-image mark of a preceding first toner image.
48. An imaging method according to claim 44 and further
comprising
rewinding a preselected length of the continuous substrate through
the second transfer region following transferring of each second
image.
49. An imaging method according to claim 48 and further comprising
accelerating the continuous substrate to a surface velocity
comparable with that of the image bearing surface before
transferring of each second image.
50. An imaging method according to claim 49 and further comprising
detecting the post image marks on the first substrate surface
between the first transfer region and the second transfer
region.
51. An imaging method according to claim 50 and further comprising
triggering the transferring of each second image in response to the
post-image mark of the preceding second image.
52. An imaging method according to claim 44 and further comprising
cutting the continuous substrate at the spaces between the first
images on the first substrate surface.
53. An imaging method according to claim 52 and further comprising
detecting the post image marks on the first substrate surface
downstream of the second transfer region.
54. An imaging method according to claim 52 and wherein cutting the
continuous substrate comprises cutting the continuous substrate in
response to detection of the post-image marks.
55. An imaging method according claim 44 and further comprising
monitoring the position of the continuous substrate relative to the
first transfer region.
56. An imaging method according to claim 55 wherein detecting the
post-image marks on the continuous substrate ahead of the first
transfer region comprises detecting the post-image marks only
within preset, first, detection time windows.
57. An imaging method according to claim 56 and further comprising
setting the time gaps between said first detection time windows in
accordance with the monitored position of the continuous substrate
relative to the first transfer region.
58. An imaging method according to claim 55 and further comprising
monitoring the position of the continuous substrate relative to the
second transfer region.
59. An imaging method according to claim 58 wherein detecting the
post-image marks on the continuous substrate between the first and
second transfer regions comprises detecting the post-image marks
only within preset, second, detection time windows.
60. An imaging method according to claim 59 and further comprising
setting the time gaps between said second detection time windows in
accordance with the monitored position of the continuous substrate
relative to the second transfer region.
61. An imaging method according to claim 37 wherein the image
bearing surface comprises an imaging surface on which a latent
image has been developed.
62. An imaging method according to claim 61 herein the imaging
surface comprises a photoreceptor surface.
63. An imaging method according to claim 37 wherein the imaging
device comprises an intermediate transfer member and wherein the
image bearing surface comprises a surface of the intermediate
transfer member.
Description
FIELD OF THE INVENTION
The present invention relates generally to improvements in imaging
apparatus and, more particularly, to imaging on both sides of a
substrate.
BACKGROUND OF THE INVENTION
There are various applications for imaging on both sides of a
substrate such as paper Today, double sided imaging is generally
carried out by a system including first and second imaging devices,
wherein one side of the substrate is imaged by the first imaging
device and the opposite side of the substrate is imaged by the
second imaging device. It is appreciated, however, that the use of
two imaging devices configured for double-sided printing is
expensive and highly space consuming.
If the substrate is provided in sheets having predetermined
dimensions adapted for a given page layout, it is possible to image
both sides of each sheet by, first, feeding the sheet with a first
surface interfacing the imaging device and, then, refeeding the
sheet with the second, opposite, surface facing the imaging device.
This method is not available for web-fed imaging.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an
electrostatic imaging system in which a single imaging device is
used for imaging both surfaces of a web type, i.e. a continuous,
substrate.
According to a preferred embodiment of the present invention, a
first surface of a continuous substrate is fed to the imaging
device by a controlled feeding mechanism and at least one image is
formed on the first surface of the substrate. Then, by guiding the
continuous substrate through an inverter mechanism, a second,
opposite, surface of the substrate is controllably fed to the
imaging device and at least one image is formed on the second
surface of the substrate. The controlled feedings of the first and
second surfaces of the substrate are preferably synchronized so as
to control the relative locations of the images formed on the first
and second surfaces.
In a preferred embodiment of the invention, a first plurality of
images are formed on the first surface of the substrate and a
second plurality of corresponding images are formed on the second
surface of the substrate, wherein the order of imaging is adapted
to appropriately locate each of the second plurality of images
opposite a corresponding image of the first plurality of images.
Preferably, the order of imaging includes, initially, imaging a
predetermined number of images on the first surface to account for
the length of continuous substrate separating between imaging of
the first surface and imaging of the second surface and, then,
alternatingly imaging on the first and second surfaces such that
each imaging on the first surface is followed by imaging on the
second surface.
In a preferred embodiment of the invention, the imaging device
includes an intermediate transfer member (ITM) which transfers
developed toner images from an imaging surface, for example a
photoconductor surface, to the substrate. The device preferably
further includes first and second impression members, wherein the
first impression member urges the first surface of the substrate
against the ITM at a first image transfer region and the second
impression member urges the second surface of the substrate against
the ITM at a second image transfer region. According to this
preferred embodiment of the invention, a given portion of the
continuous substrate is fed, first, to the first image transfer
region and then, after being guided through the inverter mechanism,
the substrate is fed to the second image transfer region.
In a preferred embodiment of the invention, particularly suitable
for high speed imaging, an improved BID (Binary Image Development)
system is used in which selected portions of a viscous layer of
concentrated liquid toner are transferred onto the photoconductor
surface to develop latent images formed thereon. Alternatively, a
BID development system is used in which only a portion of the
thickness of the concentrated layer of toner is transferred onto
the photoconductor surface. The developed images are subsequently
transferred to the substrate, preferably via the ITM, with
substantially no toner residue remaining on the ITM.
There is thus provided in accordance with a preferred embodiment of
the invention, a system for double-sided, electrostatic imaging on
a continuous-web substrate having first and second substrate
surfaces, the system including:
an imaging device comprising an image transfer member with a
toner-image bearing surface having selectively formed thereon first
and second images; and
a web-feeder system which selectively brings the first and second
substrate surfaces into operative engagement with the toner-image
bearing surface, to transfer thereto the first and second images,
respectively, in accordance with a preselected imaging
sequence.
In a preferred embodiment of the invention, the first substrate
surface engages the toner-image bearing surface at a first
impression region and the second substrate surface engages the
toner-image bearing surface at a second impression region.
Preferably, the predetermined imaging sequence includes first
surface imaging cycles, during which cycles the first images are
transferred to the first substrate surface, and second surface
imaging cycles, during which cycles the second images are
transferred to the second substrate surface. In one embodiment of
the invention, the predetermined imaging sequence includes a
plurality of consecutive first surface imaging cycles followed by
alternating, first surface and second surface, imaging cycles.
In a preferred embodiment of the present invention, the web-feeder
system includes a first impression member which urges the
continuous substrate against the toner-image bearing surface during
each first surface imaging cycle, and a second impression member
which urges the continuous substrate against the toner-image
bearing surface during each second surface imaging cycle.
Preferably, the web-feeder system further includes a substrate
inverter, operating on the continuous substrate between the first
and second impression members, which inverts between the first and
second surfaces of the continuous substrate.
Additionally, in a preferred embodiment, the web-feeder system
includes a substrate advance mechanism operative for advancing the
continuous substrate through the first and second impression
regions.
In a accordance with a preferred embodiment of the invention, the
web-feeder system further includes a controller which controls the
advance of the continuous substrate through the first and second
impression regions, in accordance with the predetermined imaging
sequence, by controlling the operation of the substrate advance
mechanism. The controller preferably also controls the engagement
and disengagement of the first and second substrate surfaces with
the toner-image bearing surface, in accordance with the
predetermined imaging sequence, by controlling the position of the
first and second impression members relative to the toner-image
bearing surface.
In a preferred embodiment of the invention, the first images are
formed on the first substrate surface with a preselected spacing.
Preferably, the imaging device produces a post-image mark on the
space following each first image on the first substrate
surface.
In a preferred embodiment of the invention, the advancing mechanism
rewinds a preselected length of the continuous substrate through
the first impression region following each first surface imaging
cycle. Preferably, according to this embodiment, the continuous
substrate is accelerated to a surface velocity comparable with that
of the toner-image bearing surface before each first surface
imaging cycle.
Further, in a preferred embodiment of the invention, the web-feeder
system further includes a first mark detector associated with the
first substrate surface, ahead of the first impression region,
which detects the post image marks on the first substrate surface
and produces first detection signals in response thereto.
Preferably, in this embodiment of the invention, the controller
triggers each first surface imaging cycle in response to the first
detection signal of the preceding post-image mark.
In a preferred embodiment of the invention, the advancing mechanism
rewinds a preselected length of the continuous substrate through
the second impression region following each second surface imaging
cycle. Preferably, according to this embodiment, the continuous
substrate is accelerated to a surface velocity comparable with that
of the toner-image bearing surface before each second surface
imaging cycle.
Further, in a preferred embodiment of the invention, the web-feeder
system further includes a second mark detector associated with the
first substrate surface, between the first and second impression
regions, which detects the post image marks on the first substrate
surface and produces second detection signals in response thereto.
Preferably, in this embodiment of the invention, the controller
triggers each second surface imaging cycle in response to the
second detection signal of the preceding post-image mark.
In accordance with a preferred embodiment of the invention, the
web-feeder system further includes a cutter, associated with the
continuous substrate downstream of the second impression region,
which cuts the continuous substrate at the spaces between the first
images on the first substrate surface. Preferably, the web-feeder
system also includes a third mark detector associated with the
first substrate surface, ahead of the cutter, which detects the
post image marks on the first substrate surface and produces third
detection signals in response thereto. The controller preferably
activates the cutter in response to the third detection
signals.
According to a preferred embodiment of the invention, the
web-feeder system further includes at least one free-loop
arrangement which contains a variable length of the continuous
substrate. The at least one free-loop arrangement preferably
includes a first free-loop arrangement ahead of the first
impression region. The at least one free-loop arrangement
preferably further includes a second free-loop arrangement between
the first impression region and the second impression region. The
web-feeder system preferably also includes a third free-loop
arrangement, between the second impression region and the cutter,
which contains a variable length of the continuous substrate.
In a preferred embodiment of the invention, the web-feeder system
further includes a first length detector, associated with the
continuous substrate between the first and second impression
regions, which produces an electric output responsive to the
position of the continuous substrate relative to the first
impression region. The first length detector
preferably includes an encoder. In a preferred embodiment, the
controller addresses the first mark detector only within preset,
first, detection time windows and wherein the time gaps between the
first detection windows are set in accordance with the output of
the first length detector.
In a preferred embodiment, the web-feeder system further includes a
second length detector, associated with the continuous substrate
downstream of the second impression region, which produces an
electric output responsive to the position of the continuous
substrate relative to second impression region. The second length
detector includes an encoder. In a preferred embodiment, the
controller addresses the second mark detector only within preset,
second, detection time windows and wherein the time gaps between
the second detection windows are set in accordance with the outputs
of the first and second length detectors.
In a preferred embodiment of the invention, the controller
addresses the third mark detector only within preset, third,
detection time windows and wherein the time gaps between the third
detection windows are set in accordance with the output of the
second length detector.
Further, in accordance with a preferred embodiment of the present
invention there is provided a method for double-sided imaging on a
continuous-web substrate, having first and second substrate
surfaces, using an electrostatic imaging device including an image
transfer member having an toner-image bearing surface, the method
including:
providing a first toner image on the toner-image bearing
surface;
transferring the first toner image from the toner-image bearing
surface to the first substrate surface;
providing a second toner image on the toner-image bearing surface;
and
transferring the second toner image from the toner-image bearing
surface to the second substrate surface
Alternatively, in a preferred embodiment of the invention, there is
provided a method for double-sided imaging on a continuous-web
substrate, having first and second substrate surfaces, using an
electrostatic imaging device including an image transfer member
having an toner-image bearing surface, the method including:
selectively forming on the toner-image bearing surface first and
second toner images, in accordance with a preselected imaging
sequence; and
selectively transferring the first and second toner images to the
first and second substrate surfaces, respectively, in accordance
with the preselected imaging sequence. In a preferred variation of
this embodiment of the invention, selectively forming the first and
second toner images in accordance with the predetermined imaging
sequence includes, first, consecutively forming a plurality of
first toner images and, then, alternatingly forming first and
second toner images.
In a preferred embodiment of the invention, transferring the first
toner image includes transferring the first toner image at a first
impression region and wherein transferring the second toner image
includes transferring the second toner image at a second impression
region. Additionally, in a preferred embodiment of the invention,
the method including inverting the first and second substrate
surfaces of the continuous substrate between the first and second
impression regions.
In a preferred embodiment of the invention, the imaging method
further includes advancing the continuous substrate through the
first and second impression regions in accordance with the
predetermined imaging sequence.
According to a preferred embodiment of the invention, transferring
the first toner images to the first substrate surface includes
transferring the first toner images with a preselected spacing.
Preferably, in this preferred embodiment, the method further
includes producing a post-image mark on the space following each
first toner image.
In a preferred embodiment, the method further includes rewinding a
preselected length of the continuous substrate through the first
impression region following transferring of each first toner image.
Preferably, the method also includes accelerating the continuous
substrate to a surface velocity comparable with that of the
toner-image bearing surface before transferring of each first toner
image.
Additionally, in a preferred embodiment, the method includes
detecting the post image marks on the first substrate surface ahead
of the first impression region. Preferably, in this preferred
embodiment, the method also includes triggering the transferring of
each first toner image in response to the-post-image mark of the
preceding first toner image.
In a preferred embodiment, the method further includes rewinding a
preselected length of the continuous substrate through the second
impression region following transferring of each second toner
image. Preferably, the method also includes accelerating the
continuous substrate to a surface velocity comparable with that of
the toner-image bearing surface before transferring of each second
toner image.
Additionally, in a preferred embodiment, the method includes
detecting the post image marks on the first substrate surface
between the first and second impression regions. Preferably, in
this preferred embodiment, the method also includes triggering the
transferring of each second toner image in response to the
post-image mark of the preceding first toner image.
In a preferred embodiment of the invention, the imaging method
further includes cutting the continuous substrate at the spaces
between the first images on the first substrate surface.
Preferably, in this preferred embodiment, the method further
includes detecting the post image marks on the first substrate
surface downstream of the second impression region. Preferably,
cutting the continuous substrate includes cutting the continuous
substrate in response to detection of post-image marks.
In a preferred embodiment of the invention, the imaging method
further includes monitoring the position of the continuous
substrate relative to the first impression region. Preferably, in
this embodiment of the invention, detecting the post-image marks on
the continuous substrate ahead of the first impression region
includes detecting the post-image marks only within preset, first,
detection time windows. In a preferred embodiment, the imaging
method includes setting the time gaps between the first detection
time windows in accordance with the monitored position of the
continuous substrate relative to the first impression region.
In a preferred embodiment of the invention, the imaging method
further includes monitoring the position of the continuous
substrate relative to the second impression region. Preferably, in
this embodiment of-the invention, detecting the post-image marks on
the continuous substrate between the first and second impression
regions includes detecting the post-image marks only within preset,
second, detection time windows. In a preferred embodiment, the
imaging method includes setting the time gaps between the second
detection time windows in accordance with the monitored position of
the continuous substrate relative to the second impression
region.
According to one, preferred, embodiment of the present invention,
the toner-image bearing surface includes a developed imaging
surface. Preferably, the imaging surface includes a photoreceptor
surface.
According to another, preferred, embodiment of the present
invention, the imaging device includes an intermediate transfer
member and the toner-image bearing surface includes a surface of
the intermediate transfer member.
There is further provided, in a preferred embodiment of the
invention, a squeegee device for squeegeeing a first surface
comprising:
a squeegee roller having a squeegee surface, a first portion of
which engages said first surface;
a leaf spring which is applied to a second portion of said squeegee
surface to urge the squeegee roller against the first surface,
wherein the leaf spring contacts the squeegee roller along its
length at discrete regions separated by non-contacting areas.
Preferably, portions of the spring comprises a low friction
material contacting the squeegee roller at said second portion.
There is further provided, in accordance with a preferred
embodiment of the invention, a squeegee device for squeegeeing a
first surface comprising:
a squeegee roller having a squeegee surface, a first portion of
which engages said first surface;
a leaf spring which is applied to said first surface and is applied
to a-second portion of said squeegee surface to urge the squeegee
roller against the first surface, and a wire wrapped around the
leaf spring such that the wire contacts the squeegee surface at a
plurality of points along the length of the roller, said points
being separated by spaces at which no contact is made with the
squeegee roller.
Preferably, the wire comprises a low friction material, preferably,
teflon.
In a preferred embodiment of the invention, the leaf spring
contacts the squeegee roller along substantially its entire
length.
There is further provided, in accordance with a preferred
embodiment of the invention, a cleaning device for removing
residual toner from a toner-bearing surface comprising:
a first, rotating, roller having a conductive surface contacting
the toner-bearing surface with substantially zero relative motion
therebetween;
a sponge roller rotating in the same sense as that of the first
roller, wherein the sponge roller is substantially compressed by
said first roller at a region of engagement therebetween; and
a second roller which compresses said sponge roller at a region
thereof remote from said region of engagement.
In a preferred embodiment of the invention, the first roller is
biased to a voltage which attracts residual toner particles on said
toner-bearing surface to said conductive surface.
Preferably, the device includes a resilient blade engaging said
conductive surface where said surface leaves said region of
engagement and operative to remove toner from said conductive
surface.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be understood and appreciated more fully
from the following detailed description, taken in conjunction with
the drawings in which:
FIG. 1 is a schematic illustration of a system for double-sided
imaging constructed and operative in accordance with a preferred
embodiment of the present invention;
FIG. 2 is a schematic illustration of a system for multi-color,
double-sided imaging, constructed in accordance with a preferred
embodiment of the present invention;
FIG. 3 is a detailed schematic illustration of a cleaning station
constructed and operative in accordance with a preferred embodiment
of the present invention;
FIG. 4 is a detailed schematic illustration of a developer assembly
constructed and operative in accordance with a preferred embodiment
of the present invention;
FIG. 5 is a detailed schematic illustration of a web-feeder system
constructed and operative in accordance with a preferred embodiment
of the present invention;
FIG. 6 is a schematic, block diagram, illustration of circuitry for
controlling the operation of the system of FIG. 2;
FIGS. 7A and 7B are, respectively, top and perspective, schematic,
illustrations depicting a method of inverting a continuous
substrate in accordance with a preferred embodiment of the present
invention; and
FIG. 8 is a schematic flow-chart showing a preferred sequence of
operation of the web-feeder system of FIG. 5.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Reference is now made to FIG. 1 which illustrates imaging apparatus
constructed and operative in accordance with a preferred embodiment
of the present invention.
The apparatus of FIG. 1 comprises a drum 10 arranged for rotation
in a direction generally indicated by arrow 14. Drum 10 preferably
has a cylindrical photoconductive surface 16, made of selenium, a
selenium compound, an organic photoconductor or any other suitable
photoconductor known in the art. Photoconductive surface may be in
the form of a photoreceptor sheet and may use any suitable
arrangement of layers of materials as is known in the art. However,
in the preferred embodiment of the invention, certain of the layers
of photoreceptor sheet 16 are removed from the ends of the sheet to
facilitate its mounting on drum 10.
This preferred photoreceptor-sheet and preferred methods of
mounting it on drum 10 are described in a co-pending application of
Belinkov et al., PHOTORECEPTOR SHEET AND IMAGING SYSTEM UTILIZING
SAME, filed Sep. 7, 1994, assigned Ser. No. 08/301,775, now U.S.
Pat. No. 5,508,790 and corresponding applications in other
countries, the disclosure of which is incorporated herein by
reference. Alternatively, photoreceptor 16 may be deposited on drum
10 and may form a continuous surface.
When the apparatus is operated, drum 10 rotates and photoconductive
surface 16 is charged by a charger 18 to a generally uniformly
pre-determined voltage, typically a negative voltage on the order
of 1000 volts. Charger 18 may be any type of charger known in the
art, such as a corotron, a scorotron or a roller.
In a preferred embodiment of the invention, charger 18 is a double
scorotron including a housing and two corona wire segments 218.
Although desirably, particularly for high-speed imaging, the
voltage between wires 218 and surface 16 should preferably be as
high as possible, the actually obtained voltage is generally not
higher than 7000-7500 Volts, typically 7300 Volts, due to
discharging between wires 218 and housing 33. The present
invention, however, provides a method for raising the voltage
between wire segments 218 and surface 16. According to the present
invention, housing 33 is electrically insulated from other elements
of the imaging device and is charged to a relatively high voltage,
preferably on the order of 1500 Volts. This enables charging of
wires 218 to a voltage on the order of 9000 Volts, maintaining the
voltage difference between wires 218 and housing 33 within a safe
range.
Continued rotation of drum 10 brings charged photoconductive
surface 16 into image receiving relationship with an exposure means
such as a light source 19, which may be a laser scanner (in the
case of a printer) or the projection of an original (in the case of
a photocopier). In a preferred embodiment of the present invention,
imaging apparatus 19 is a modulated laser beam scanning apparatus,
or other laser imaging apparatus such as is known in the art.
Light source 19 forms a desired latent image on charged
photoconductive surface 16 by selectively discharging a portion of
the photoconductive surface, the image portions being at a first
voltage and the background portions at a second voltage. The
discharged portions preferably have a negative voltage of less than
about 100 volts.
Continued rotation of drum 10 brings charged photoconductive
surface 16, bearing the electrostatic latent image, into operative
engagement with the surface 21 of a developer roller 22 which is
part of developer assembly 23, more fully described below with
reference to FIG. 4. Developer roller 22 rotates in a direction
opposite that of drum 10, as shown by arrow 13, such that there is
substantially zero relative motion between their respective
surfaces at the point of contact. Surface 21 of developer roller 22
is preferably composed of a soft polyurethane material, preferably
made more electrically conductive by the inclusion of conducting
additives, while the core of developer roller 22 may be composed of
any suitable electrically conductive material. Alternatively, drum
10 may be formed of a relatively resilient material, and in such
case surface 21 of developer roller 22 may be composed of either a
rigid or a compliant material. Developer roller 22 is preferably
charged to a negative voltage of approximately 300-600 volts,
desirably approximately -400 volts.
As described below, surface 21 is coated with a very thin layer of
concentrated liquid toner, preferably containing 20-50% charged
toner particles, more preferably 25% solids or more. The layer is
preferably between 5 and 30 .mu.m, more preferably between 5 and 15
.mu.m, thick.
Developer roller 22 itself is charged to a voltage that is
intermediate the voltage of the charged and discharged areas on
photoconductive surface 16.
In a preferred embodiment of the invention, a liquid toner similar
to the toner described in Example 1 of U.S. Pat. No. 4,794,651, the
disclosure of which is incorporated herein by reference, is used
although other types of toner are usable in the invention. For
colored toners the carbon black in the preferred toner is replaced
by colored pigments as is well known in the art. The liquid toner
is preferably maintained in a toner reservoir 65 which is
associated with development assembly 23.
When surface 21 of developer roller 22 bearing the layer of liquid
toner concentrate is engaged with photoconductive surface 16 of
drum 10, the difference in voltages between developer roller 22 and
photoconductive surface 16 causes the selective transfer of the
layer of toner particles to photoconductive surface 16, thereby
developing the desired latent image. Depending on the choice of
toner charge polarity and the use of a "write-white" or
"write-black" system, the layer of toner particles will be
selectively attracted to either the charged or discharged areas of
photoconductive surface 16, and the remaining portions of the toner
layer will continue to adhere to surface 21 of developer roller
22.
Because the transfer of the concentrated layer of toner is much
less mobility dependent than in normal electrophoretic development,
the process described above occurs at a relatively high speed.
Also, since the layer already has a high density and viscosity,
there is no need to provide for metering devices, rigidizing
rollers and the like which would otherwise be necessary to remove
excess liquid from the developed image to attain the desired
density of toner particles of the developed image.
For multicolor systems, as shown in FIG. 2, a plurality of
development assemblies 23A-23D may be provided, one for each color
of the multi-color image. According to this embodiment of the
invention, assemblies 23A-23D sequentially engage photoconductive
surface 16 to develop sequentially produced latent images thereon.
Assemblies 23A-23D may be combined into an integrated, multi-color,
development assembly 63.
The present invention is described in the context of a BID (Binary
Image Development) system in which the concentrated layer of liquid
toner is completely transferred to photoconductor surface 16 during
development. However, it should be appreciated that the present
invention is also compatible with a partial BID system in which
only a portion of the thickness of the concentrated toner layer is
transferred to surface 16 by appropriately adjusting the
development voltages. A preferred partial BID system of this type
is described in PCT publication WO 94/16364, the disclosure of
which is incorporated herein by reference.
Downstream of development assembly 23, as shown in FIGS. 1 and 2, a
preferred embodiment of the imaging apparatus further includes a
background discharge device 28. Discharge device 28 is operative to
flood the surface 16 with light which discharges the voltage
remaining on surface 16, mainly to reduce electrical breakdown and
improve subsequent transfer of the image. Operation of such a
device in a write black system is described in U.S. Pat. No.
5,280,326, the disclosure of which is incorporated herein by
reference.
The latent image developed by means of the process described above
may then be directly transferred to a desired substrate in a manner
well known in the art. Alternatively, as in the preferred
embodiments of the invention shown in FIGS. 1 and 2, the developed
image is transferred to the desired substrate via an intermediate
transfer member 40, which may be a drum or belt, in operative
engagement with photoconductive surface 16 of drum 10 bearing the
developed image. Intermediate transfer member 40 rotates in a sense
opposite to that of photoconductive surface 16, as shown by arrow
43, providing substantially zero relative motion between their
respective surfaces at the point of image transfer.
Intermediate transfer member 40 is operative for receiving the
toner image from photoconductive surface 16 and for transferring
the toner image to a final substrate 42, such as paper. Final
substrate 42, which is preferably continuously fed as described
below, is urged against the image bearing surface of ITM 40 by
either a first impression roller 39 or a second impression roller
41, in accordance with a predetermined imaging sequence, as
described in detail below. The transfer of the toner image from ITM
40 to substrate 42 is preferably electrostatically assisted by
charging impression rollers 39 and 41 to an appropriate voltage,
which is adapted to counteract the electrostatic attraction of the
toner image to ITM 40. In a preferred embodiment of the invention,
substrate 42 engages ITM 40 at a first impression region 239, when
urged by roller 39, and at a second impression region 241, when
urged by roller 41. Impression rollers 39 and 41 form part of a
web-feeder system 100 which is described below with reference to
FIG. 5.
Disposed internally of intermediate transfer member 40 there may be
provided a heater 45, to heat intermediate transfer member 40 as is
known in the art. Transfer of the image to intermediate transfer
member 40 is preferably aided by providing electrification of
intermediate transfer member 40 to provide an electric field
between intermediate transfer member 40 and the image areas of
photoconductive surface 16. Intermediate transfer member 40
preferably has a conducting layer 44 underlying an elastomer layer
46, which is preferably a slightly conductive resilient polymeric
layer.
Intermediate transfer member (ITM) 40 may be any suitable
intermediate transfer member, for example, as described in U.S.
Pat. Nos. 4,684,238 and 4,974,027 or in PCT Publication WO
90/04216, the disclosures of which are incorporated herein by
reference. Alternatively, in a preferred embodiment of the
invention, ITM 40 has a multilayered transfer portion such as those
described below or in U.S. Pat. Nos. 5,089,856 and 5,047,808, or in
U.S. patent application Ser. No. 08/371,117, filed Jan. 11, 1995,
now U.S. Pat. No. 5,745,829 and entitled IMAGING APPARATUS AND
INTERMEDIATE TRANSFER BLANKET THEREFOR and corresponding
applications in other countries, the disclosures of all of which
are incorporated herein by reference. Member 40 is maintained at a
suitable voltage and temperature for electrostatic transfer of the
image thereto from image bearing surface 16.
In accordance with a preferred embodiment of the invention, after
developing each image in a given color, the single color image is
transferred to intermediate transfer member 40. Subsequent images
in different colors are sequentially transferred in alignment with
the previous image onto intermediate transfer member 40. When all
of the desired images have been transferred thereto, the complete
multi-color image is transferred from transfer member 40 to
substrate 42. Impression rollers, 39 or 41, produce operative
engagement between intermediate transfer member 40 and substrate 42
at regions 239 or 241, respectively, when transfer of the composite
image to substrate 42 takes place.
While the embodiment of the invention in which all the colors are
transferred is most preferred, each single color image can be
separately transferred to the substrate via the intermediate
transfer member. In this case, the substrate may be fed through the
imaging device once for each color, using dual-feeder system 100.
Alternatively, the intermediate transfer member can be omitted and
the developed single color images transferred sequentially directly
from surface 16 of drum 10 to substrate 42.
It should be understood that the invention is not limited to the
specific type of image forming system used and the present
invention is also useful with any suitable imaging system which
forms a liquid toner image on an image forming surface, such as
that shown in the above referenced patent application Ser. No.
08/371,117, now U.S. Pat. No. 5,745,829 and, for some aspects of
the invention, with powder toner systems. Furthermore some aspects
of the invention are suitable for use with offset printing systems
as are well known in the art. The specific details given above for
the image forming system are included as part of a best mode of
carrying out the invention, however, many aspects of the invention
are applicable to a wide range of systems as known in the art for
electrostatic and offset ink printing and copying.
Following the transfer of the toner image to substrate 42 or to
intermediate transfer member 40, photoconductive surface 16 engages
a cleaning station 49 which may be any cleaning station known in
the art. However, in a preferred embodiment of the invention,
cleaning station 49 is an improved cleaning station which also
functions as a cooling station, as described below with reference
to FIG. 3.
According to the preferred embodiment of FIG. 3, cleaning station
49 includes a casing 81 which is associated with a carrier liquid
inlet 90 and a carrier liquid outlet 92. Carrier liquid inlet 90
preferably includes a perforated nozzle 191 which disperses the
supplied carrier liquid. Fresh and, preferably, cooled carrier
liquid is preferably pumped from a carrier liquid reservoir (not
shown) to inlet 90 which scatters the liquid in the direction of a
wet cleaning roller 88. Wet cleaning roller 88 is preferably formed
of a relatively rigid material, such as metal, and is mounted
juxtaposed with surface 16 of drum 10, preferably with a gap of 120
to 150 micrometers from surface 16. Roller 88, which preferably has
a diameter of approximately 22 millimeters, is preferably rotated
in the same sense as that of drum 10, such that their respective
surfaces move in opposite directions at the region of interface. In
a preferred embodiment of the invention, the linear velocity of
surface 16 is between 60 and 150 centimeters per second, and the
surface velocity of roller 88 is equal to approximately 80 percent
of the velocity of surface 16. This relative motion in combination
with the constant supply of fresh carrier liquid from the reservoir
results in thorough wetting of surface 16. The constant supply of
fresh carrier liquid from inlet 90 is also operative to cool
surface 16 of drum 10, so as to counteract heating of surface 16 by
other elements of the imaging apparatus, such as the ITM.
The toner on surface 16, which is now diluted in the wetting
carrier liquid, is carried by surface 16 of drum 10 towards a
sponge roller 82 which is urged against surface 16, such that the
surface of roller 82 is deformed inwardly by approximately 1.5
millimeters. Sponge roller 82, which is preferably constructed of
an approximately 4 millimeter layer of open-cell polyurethane
around a metal core having a diameter of approximately 14
millimeters, absorbs the diluted toner and scrubs it off surface
16. As shown in FIG. 3, sponge roller 82 preferably rotates in the
same sense as that of drum 10, such that their respective surfaces
move in opposite directions at their region of contact.
A squeezer roller 84 which is urged deeply into sponge roller 82,
preferably to a depth of approximately 2 millimeters from the
original surface of roller 82, squeezes used carrier liquid out of
roller 82. Squeezer 84, which is preferably a metal roller having a
diameter of approximately 16 millimeters, is preferably an idler
roller, i.e. rotates in response to the rotation of sponge roller
82. A scraper 56, preferably a resilient blade urged against
surface 16 next to sponge roller 82, completes the removal of any
residual toner on surface 16 which may have not been removed by
sponge roller 82. Blade 56 is preferably formed of polyurethane and
has a thickness of approximately 3 millimeters.
The used carrier liquid squeezed out of roller 82 is drained by
free-fall, along the surface of a fluid guide 86 which separates
the relatively warm and soiled carrier liquid from the fresh
carrier liquid supplied by inlet 90, back to the liquid toner
reservoir via carrier liquid outlet 92. Fluid guide 86 is
preferably resiliently urged against the surface of roller 88 via
a, preferably spongy, sealing pad 87. Fluid guide 86 is preferably
formed of metal and sealing pad 87 is preferably formed of
closed-cell polyurethane.
A lamp 58 completes the imaging cycle by removing any residual
charge, characteristic of the previous image, from photoconductive
surface 16, if necessary. In some embodiments of the present
invention, lamp 58 may be omitted and surface 16 is discharged only
by discharge device 28, as described above with reference to FIG. 1
and FIG. 2.
It is to be understood that, in a preferred embodiment of the
invention, the liquid toner concentrate which is transferred to
drum 10 has substantially the same toner particle concentration as
the image when it is transferred from drum 10. This is in contrast
to traditional liquid development where the liquid developer has a
comparatively low concentration of particles before development and
where excess liquid is removed from the image before transfer from
the photoconductor. It is also in contrast to U.S. Pat. No.
4,504,138, in which the toner supplied to the drum is more
concentrated, but where excess liquid must still be removed from
the image before transfer to the final substrate. In a preferred
embodiment of the present invention, the toning material developed
onto drum 10 is at a solids concentration substantially equal to
that of the image transferred from the drum. Since the toner
supplied during development to surface 21 of developer roller 22 is
generally not sufficiently concentrated, the toner on surface 21 is
further concentrated before contact with drum 10, for example by
mechanical and electrical squeegeeing as described below with
reference to FIG. 4.
In addition to the details of the imaging methods and apparatus
given above, additional details of imaging processes and devices
are given in the patents and publications incorporated herein by
reference.
Reference is now made to FIG. 4 which schematically illustrates the
construction and operation of developer assembly 23. Developer
assembly 23, including developer roller 22 and other elements
described below, may be a fixed component within the imaging
apparatus or, alternatively, assembly 23 may take the form of a
replaceable cartridge (not shown) which is readily inserted into
the housing of the imaging apparatus and removed therefrom when the
supply of liquid toner concentrate has been depleted.
As shown in FIG. 4, assembly 23 preferably includes a housing 60
having a toner inlet 62 and a toner outlet 64 which are associated
with toner reservoir 65. In accordance with a preferred embodiment
of the invention, the liquid toner in reservoir 65 contains up to 8
percent charged toner particles, preferably 1.8-2 percent, and
carrier liquid. Fresh liquid toner from container 65 is preferably
pumped via toner inlet 62 into an inlet chamber 63 of assembly 23
by a pump (not shown), and unused toner is returned from housing 60
to reservoir 65 via toner outlet 64. In multi-color systems, as
shown in FIG. 2, assemblies 23A-23D of multi-color development
assembly 63 are associated with respective reservoirs 65A-65D, each
reservoir containing a different color toner.
As described above, developer roller 22, which is mounted within
housing 60, is preferably composed of any suitable electrically
conducting material and has a surface composed of a soft
polyurethane material, preferably made more electrically conductive
by the inclusion of conducting additives. In a preferred embodiment
of the invention roller 22 has a small diameter, desirably less
than 4 cm and preferably approximately 30 millimeters. Preferably,
developer roller 22 includes a metal core, having a diameter of
approximately 26 millimeters, coated with a 1.95 millimeter layer
of polyurethane having a Shore A hardness of 20. The polyurethane
layer is preferably coated with a 4-5 micrometer layer of a
conductive lacquer which also extends along the sides of roller 22
so as to be electrically connected to the metal core. The
conductive lacquer preferably includes three parts H322 (Lord
Corporation, U.S.A.) and 1 part ethyl acetate, however, other
conductive lacquers may be suitable. The conductive layer is
preferably coated with an additional layer of polyurethane,
preferably having a Shore A hardness of 20-25 and a resistivity on
the order of 1.multidot.10.sup.8 .OMEGA..multidot.cm.
The surface of roller 22 protrudes somewhat from the opening of
housing 60 such that, when assembly 23 is installed in the imaging
apparatus, surface 21 of roller 22 is in contact with
photoconductive surface 16 of drum 10. When the apparatus is
activated, roller 22 is electrically charged, preferably to a
negative voltage of 300-600 volts, for example -400 volts, and is
rotated in the direction indicated by arrow 13. A layer of highly
concentrated liquid toner is deposited on surface 21 of roller 22,
as described below, and thus, roller 22 functions as a developer
roller with regard to latent images formed on photoconductive
surface 16 of drum 10, as described above with reference to FIG.
1.
In a preferred embodiment of the invention, the pressurized toner
received via inlet 62 is deposited on developer roller 22 by a
depositing electrode 70 which forms one wall of inlet chamber 63.
The opposite wall 72 of inlet chamber 63 is preferably formed of an
insulating material, for example a plastic insulator, and is
juxtaposed with surface 21 by a distance of approximately 0.5
millimeters. Electrode 70, which is preferably charged to a
negative voltage of 900-2000 volts, for example -1400 volts, is
preferably situated juxtaposed with a portion of developer roller
22, preferably at a distance of approximately 400 micrometers
therefrom. The large difference in voltage between electrode 70 and
developer roller 22 causes toner particles to adhere to developer
roller 22, while the generally neutral carrier liquid is generally
not affected by the voltage difference. The deposited liquid toner
is carried by surface 21 of roller 22 in the direction indicated by
arrow 13. The layer of liquid toner deposited on surface 21 is
preferably at a concentration of 15-17 percent as described
below.
In addition to developer roller 22 and electrode 70, assembly 23
includes a squeegee roller 66 and a cleaning roller 74 which are
mounted within housing 60 in contact with the surface of developer
roller 22. Rollers 66 and 74 are composed of any suitable
electrically conducting material, preferably metal, having a smooth
surface. The diameters of squeegee roller 66 and cleaning roller 74
are preferably significantly smaller than that of developer roller
22. Thus, if the diameter of roller 22 is approximately 3
centimeters, the diameters of rollers 66 and 74 are preferably
approximately 10 millimeters.
When the imaging apparatus is operated, rollers 66 and 74 are
electrically charged and are caused to rotate in a sense opposite
that of roller 22, as indicated by arrows 67 and 73, while being
urged against the resilient surface of roller 22. In a preferred
embodiment of the invention, squeegee roller 66 is charged to a
negative voltage of 400-800 volts, preferably approximately -600
volts, and cleaning roller 74 is preferably charged to a negative
voltage of 0-200 volts.
Squeegee roller 66 is preferably urged against roller 22, at a
pressure of approximately 100 grams per centimeter of length, by
means of a leaf spring 68, preferably extending along substantially
the entire length of the squeegee roller and having a, preferably
teflon, tip which engages the surface of roller 66. The tip is
preferably formed with grooves in the direction of motion of the
surface of roller 66 which prevent accumulation of toner between
roller 66 and spring 68 by allowing draining of the toner
therefrom.
Alternatively as shown in FIG. 4, the leaf spring includes a wire,
preferably of a low friction material such as teflon, wrapped
around the leaf as around a core to form a flat coil with an axis
along the length of the squeegee roller. The wires are spaced in
the winding direction so that they contact the squeegee roller only
along discrete portions or points along its length so that the
above described draining of toner may occur. Preferably, the spring
is formed with spaced winding grooves to position the wire and
stabilize its position.
Squeegee roller 66 is operative to squeegee excess carrier liquid
from surface 21 of developer roller 22, thereby to further increase
the concentration of solids on surface 21. Because of the squeegee
action at the region of contact between resilient surface 21 and
the surface of squeegee roller 66, a large proportion of the
carrier liquid contained within the toner concentrate is squeezed
out of the layer, leaving a layer having a solids concentration of
20 percent or more as described below. The excess carrier liquid,
which may include a certain amount of toner particles, drains
towards toner outlet 64.
Preferably, the ends of squeegee roller 66 and roller 22 are formed
with matching chamfered ends to reduce the effects of end overflow.
Such chamfered rollers are described more fully in a PCT
application titled "Squeegee roller for Imaging Systems" which
corresponds to Israel application 111441, filed Oct. 28, 1994. This
PCT application, which is incorporated herein by reference, is
filed on the same day as the present application.
Cleaning roller 74, by virtue of the relatively low voltage to
which it is charged, is operative to remove residual toner from
surface 21 of developer roller 22. The toner collected by roller 74
is then preferably scraped off roller 74 by a, preferably
resilient, cleaning blade 76 which is urged against the surface of
roller 74. The scraped toner is preferably absorbed by a sponge
roller 78, which is urged against roller 74 so as to be slightly
deformed thereby, preferably by approximately 1.5 millimeters
radially. Sponge roller 78 rotates in the same sense as that of
roller 74, such that the surfaces of rollers 74 and 78 move in
opposite directions at their region of contact. Sponge roller 78
also absorbs some of the excess liquid toner from the deposition
region between electrode 70 and roller 22, mainly including carrier
liquid, which is drained along the external surface of insulator
wall 72 of chamber 63. Roller 78 preferably has a diameter of
approximately 20 millimeters and is preferably formed of open-cell
polyurethane surrounding a metal core having a diameter of
approximately 8 millimeters.
Finally, some of the toner particles and carrier liquid absorbed in
sponge roller 78 is squeezed out of the sponge roller by a
relatively rigid squeezer roller 80, which is preferably urged
deeply into sponge roller 78, desirably approximately 2 millimeters
radially. Squeezer roller 80 is preferably an idler roller which
rotates in response to the rotation of sponge roller 78.
In a preferred embodiment of the invention, the layer deposited on
surface 21 of roller 22 has a very high solids concentration,
preferably greater than about 15 percent and typically between 15
and 17 percent, depending on which color toner is deposited. This
concentration is much higher than the initial concentration of
solids supplied to inlet 62 from reservoir 65, which concentration
is generally lower than 8 percent solids and typically between 1.8
and 2 percent solids. Squeegeeing of the deposited layer of toner
by squeegee roller 65, as described above, further increases the
concentration of solids in the toner layer to approximately 20-50
percent solids, depending on the color of the toner. This high
concentration has been found to be almost dry to the touch,
non-flowing and crumbly in texture. It has also been found that the
quality of the developed latent image is enhanced greatly as a
result, and no additional drying mechanism is needed when the image
is transferred to final substrate 42. Since so much liquid has been
removed from the layer, a thickness of 2-8 micrometers on surface
21 of roller 22 is sufficient.
As roller 22 continues to rotate and interfaces the
latent-image-bearing surface of drum 10, portions of the layer of
the dry to the touch liquid toner concentrate are selectively
transferred to surface 16 of drum 10, thereby developing the latent
image as explained above.
After portions of the layer of toner concentrate have been
transferred to surface 16 of drum 10 to develop the latent image,
the remaining portions of the toner layer on roller 22 continue to
rotate on surface 21 until they reach the region of contact with
cleaning roller 74. As described above, the relative electrical
potentials on roller 22 and roller 74, cause the remaining portions
of the toner layer to be transferred to roller 74. Resilient blade
76, which is preferably anchored to housing 60, scrapes off the
remaining portions of the toner layer from the surface of roller
74, as described above.
Although a variety of toners are suitable for the present
invention, the following toner materials and toner production
methods are preferred:
COMPOUNDING
Black, Yellow and Magenta Toners:
10,500 g. of Nucrel 925 resin and 10,500 g. of Isopar-L are charged
in a Ross Double Planetary Mixer LDM, 10 gallons. Mixing starts at
a speed control setting of 2 and the oil temperature in the heating
unit is set to 300.degree. F. After 1 hour of mixing, 9,000 g. of
Isopar-L, preheated to 120.degree. C., are added. The speed control
setting is raised to 5 for an additional hour. Then the heating
unit is turned off and the system gradually cools, for
approximately 4 hours, until the temperature of the mixture drops
below 45.degree. C., while mixing is maintained at a speed control
setting of 5.
Cyan Toner:
7,500 g. of Bynel 2002 resin and 7,500 g. of Isopar-L are charged
in a Ross Double Planetary Mixer LDM, 10 gallons. Mixing starts at
a speed control setting of 2 and the oil temperature in the heating
unit is set to 300.degree. F. After 1 hour of mixing, 15,000 g. of
Isopar-L, preheated to 120.degree. C., are added. The speed control
setting is raised to 5 for an additional hour. Then the heating
unit is turned off and the system gradually cools, for
approximately 4 hours, until the temperature of the mixture drops
below 45.degree. C., while mixing is maintained at a speed control
setting of 5.
GRINDING
Black Toner:
The following materials are mixed in a 30S Union Process attritor,
equipped with 3/16" carbon steel balls, at a low speed setting of
2:
17,828.6 g. of the compounding material described above;
1,560.0 g. of Mogul-L (carbon black by Cabot);
156.0 g. of BT583D (blue pigment by Cookson);
117.0 g. of Aluminum Stearate (by Riedl de Haen); and
32,611.4 g. of Isopar-L (by Exxon).
Grinding of the mixture starts at a speed control setting of 6, for
approximately 2 hours, until the mixture reaches a temperature of
approximately 58-60.degree. C. The attritor is then cooled to a
temperature of approximately 42.+-.2.degree. C., while the same
grinding speed is maintained. The grinding is stopped after a total
grinding period of 22 hours.
Yellow Toner:
The following materials are mixed in a 15S Union Process attritor,
equipped with 3/16" carbon steel balls, at a low speed setting of
2:
7,200.0 g. of the compounding material described above;
480.0 g. of Sicofast Yellow D1355DD (by BASF);
67.5 g. of Aluminum Stearate (by Riedl de Haen); and
12,252.0 g. of Isopar-L (by Exxon).
Grinding of the mixture starts at a speed control setting of 5.5,
for approximately 2 hours, until the mixture reaches a temperature
of approximately 55.degree. C. The attritor is then cooled to a
temperature of approximately 34.+-.2.degree. C., while the same
grinding speed is maintained. The grinding is stopped after a total
grinding period of 22 hours.
Magenta Toner:
The following materials are mixed in a 1S Union Process attritor,
equipped with 3/16" carbon steel balls, at a low speed setting of
2:
669.3 g. of the compounding material described above;
14.86 g. of R6300 (pigment by Mobay);
29.64 g. RV6803 (pigment by Mobay);
6.3 g. of Aluminum Stearate (by Riedl de Haen); and
1,250.0 g. of Isopar-L (by Exxon).
The mixture is ground for approximately 20 hours at a temperature
of approximately 40.+-.3.degree. C.
Cyan Toner:
The following materials are mixed in a 30S Union Process attritor,
equipped with 3/16" carbon steel balls, at a low speed setting of
2:
10,440 g. of the compounding material described above;
390 g. of BT583D pigment (by Cookson);
6 g. of Sicofast Yellow D1355DD (by BASF);
45 g. of Aluminum Stearate (by Riedl de Haen); and
9,125 g. of Isopar-L (by Exxon).
Grinding of the mixture starts at a speed control setting of 6, for
approximately 1.5 hours, until the mixture reaches and does not
exceed a temperature of approximately 55.degree. C. The attritor is
then cooled to a temperature of approximately 34.+-.4.degree. C.,
while the same grinding speed is maintained. The grinding is
stopped after a total grinding period of 24 hours.
MAGNETIC TREATMENT
Black, Yellow, Magenta and Cyan Toners:
The ground toner is taken out of the attritor and placed in an
adequate container, where it is diluted to a concentration of
approximately 5% solids. Two strong magnets, preferably
approximately 12,000 Gauss each, are associated with the bottom of
the container The diluted toner is then mixed at approximately 150
RPM for approximately 2 hours.
CONCENTRATION
Black, Yellow, Magenta and Cyan Toners:
The magnetically treated toner is placed in a vacuum nutcha, such
as a Buchner Funnel, having a polypropylene cloth support, and is
concentrated using a vacuum pump. The toner concentration exceeds
22% solids after approximately 4 hours of pumping.
CHARGING
Black, Yellow, Magenta and Cyan Toners:
The concentrated toner is placed in a planetary mixer. A
predetermined amount of charge director is added, preferably
approximately 9 milligrams charge director per gram of toner
solids. The toner concentration is adjusted, using Isopar-L, to
approximately 20% solids. The toner is then pumped into 380 gram
containers using a gear pump system. A variety of charge directors
known in the art are operative in this embodiment of the invention.
A preferred charge director for the present invention, preferably
utilizing lecithin, BBP and ICIG3300B, is described in U.S. patent
application 07/915,291, now U.S. Pat. No. 5,346,796 and in P.C.T.
Publication W.O. 94/02887.
To obtain a concentration of generally less than 8 percent solids,
and preferably 1.8-2, as required by the preferred imaging
apparatus described above, each toner concentrate is diluted by a
predetermined amount of carrier liquid. The toner is generally
diluted with Isopar-L type carrier liquid but may additionally
include 1-2 percent of Marcol-82. In some embodiments of the
invention, the carrier liquid may be at least partially replaced by
a grease or petroleum which has a high viscosity and is
thixotropic, thereby reducing leaks.
Reference is now made to FIG. 5, which schematically illustrates a
preferred embodiment of web-feeder system 100, and to FIG. 6 which
schematically illustrates, in block diagram form, a preferred
circuit for controlling the operation of web-feeder system 100.
Reference is also made to the flow-chart of FIG. 8 which
schematically illustrates a preferred sequence of operation of
web-feeder system 100. As described above, with reference to FIG.
1, web-feeder system 100 includes first and second impression
rollers 39 and 41 which are alternatively applied to support final
substrate 42 against the surface of ITM 40 at regions 239 and 241,
respectively.
According to the present invention, as described in detail below, a
first surface 101 of substrate 42 engages ITM 40 when roller 39 is
urged against the ITM, and a second, opposite surface 103 of
substrate 42 engages ITM 40 when roller 41 is urged against the
ITM. This arrangement enables imaging on both surfaces 101 and 103
of substrate 42 using a single imaging apparatus, wherein ITM 40
engages surfaces 101 and 103 in accordance with a predetermined
imaging sequence, as described below. Rollers 39 and 41 are driven
by impression motors 156 and 162, the operation of which is
controlled by a controller 150.
Substrate 42, which may be formed of paper or any other suitable
material, is preferably a continuous web supplied from a
web-dispenser roll 102, through a substrate input arrangement which
preferably includes input roller 104 and 105. Input rollers 104 and
105 are preferably driven by an input motor 152, the operation of
which is controlled by controller 150 as described below. It should
be appreciated that first surface 101, as defined above, is the top
surface of continuous substrate 42 when the substrate is between
rollers 104 and 105.
The dispensed continuous web 42 is guided to a first free-loop
arrangement
107, having maximum height detectors 106 and minimum height
detectors 108 associated with controller 150. Detectors 106 are
activated when the loop of substrate 42, dispensed into arrangement
107, is above a predetermined maximum height, while detectors 108
are activated when the loop of substrate 42 in arrangement 107 is
below a predetermined minimum height. When detectors 106 are
activated, controller 150 activates motor 152 so as to dispense
more of web 42 from dispenser 102 into loop arrangement 107,
thereby to lower the loop in arrangement 107. When detectors 108
are activated, controller 150 deactivates motor 152 so as to stop
dispenser 102 from dispensing web 42 into loop arrangement 107,
thereby to raise the loop in arrangement 107. In this manner, the
length of substrate 42 in loop arrangement 107 is maintained within
a predetermined length range which allows sufficient timing
flexibility during imaging.
Continuous web 42 is pulled out of free loop arrangement 107, via a
support roller 110, by a collection arrangement which preferably
includes tension rollers 112 and 113. Rollers 112 and 113 are
preferably driven by a tension motor 154 which is controlled by
controller 150. Motor 154 is preferably a torque motor operative
for maintaining a substantially constant tension in web substrate
42, downstream of rollers 112 and 113, during operation of the
web-feeder system.
Downstream of tension rollers 112 and 113, web 42 passes a first
detector 114 which is operative for detecting image synchronization
marks which are imprinted between images, as described below.
Downstream of detector 114, web 42 is supported by impression
roller 39 which is driven by an impression motor 156 which, in
turn, is activated by controller 150 according to the predetermined
imaging sequence. In accordance with a preferred embodiment,
impression roller 39 is urged towards impression region 239 of ITM
40 only when first surface 101 of web 42 is to be imaged according
to the imaging sequence. In a preferred embodiment, each period of
engagement between surface 101 with ITM 40, i.e. each first surface
imaging cycle, is initiated by a First Image Trigger signal from
controller 150.
According to a preferred embodiment of the invention, before each
first surface imaging cycle, web 42 is accelerated by motor 156 and
by an indexing motor 158 which is described below, until the
velocity of surface 101 is comparable with the surface velocity of
ITM 40. This allows position controlled, slip-free, engagement
between surface 110 and ITM 40 during imaging on the-first surface.
Further, in a preferred embodiment, a preselected post-image mark
is imprinted on surface 101 immediately following each image
printed thereon. This mark is detectable by first detector 114 and
by second and third detectors, 128 and 144, as described in detail
below.
In a preferred embodiment, web 42 is partially rewound, preferably
by reverse operation of motors 154, 156 and 158, after each first
surface imaging cycle. This provides a length of web as necessary
for subsequent reacceleration of web 42 for the next first surface
imaging cycle. Correct positioning of a given first surface image
is enabled by detection of the post-image mark of the preceding
first surface image. To prevent false detection of the post-image
marks, detector 114 is preferably operative only within preset
detection time windows, during which time controller 150 queries
for a detection signal. The time gaps between consecutive detection
time windows are preferably set in accordance with the page layout
of the respective first surface images.
In a preferred embodiment of the invention, the first surface
images are reproduced with a minimal spacing, preferably not more
than a few millimeters, whereby the post-image marks are imprinted
within the boundaries of the spacings. To account for varying page
layouts, the images on ITM roller 40 are preferably
bottom-justified, such that a substantially constant spacing is
maintained between images. It should be appreciated, however, that
in an alternative embodiment of the invention pre-image marks may
be used rather than post-image marks and, in such an embodiment,
the images on the surface of ITM 40 are preferably
top-justified.
Web 42, bearing images on first surface 101 thereof, then passes
through indexing rollers 116 and 117 which are, preferably, driven
by first indexing motor 158. Indexing motor 158 communicates with
controller 150 and is operative, together with motor 156, to
advance web 42 in accordance with the first surface imaging cycles,
i.e. for a specified length of web 42 after each First Image
Trigger signal generated by controller 150. The velocity and
relative position of web 42 during each first surface imaging cycle
are preferably monitored by controller 150 through an encoder which
is preferably associated with rollers 116 and 117.
Downstream of indexing rollers 116 and 117, continuous web 42 is
guided into a second free-loop arrangement 119, having maximum
height detectors 118 and minimum height detectors 120 associated
with controller 150. Detectors 118 are activated when the loop of
substrate 42 dispensed into arrangement 119 is above a
predetermined maximum height, while detectors 120 are activated
when the loop of substrate 42 in arrangement 119 is below a
predetermined minimum height. When detectors 120 are activated,
controller 150 activates a second tension motor 160 which drives
second tension rollers 124 and 125, downstream of loop arrangement
119, to collect web 42 from loop arrangement 119 thereby to raise
the loop in arrangement 119. When detectors 118 are activated,
controller 150 deactivates motor 160 so as to stop tension rollers
124 and 125 from collecting web 42 from loop arrangement 119,
thereby to lower the loop in arrangement 119. In this manner, the
length of substrate 42 in loop arrangement 119 is maintained within
a predetermined length range which allows sufficient imaging timing
flexibility.
Motor 160 is preferably a torque motor which maintains a
substantially constant tension in web substrate 42, downstream of
rollers 124 and 125, during operation of the web-feeder system. Web
42 is preferably collected from second loop arrangement 119 via a
support roller 122 similar to support roller 110.
Downstream of roller 122, web 42 enters an inverter mechanism 130
which inverts substrate 42 such that, at the exit of inverter 130,
first surface 101 becomes the bottom surface of substrate 42 and
surface 103 becomes the top surface thereof. Reference is now made
also to FIGS. 7A and 7B which schematically illustrates inversion
of continuous substrate 42 in accordance with a preferred
embodiment of the present invention.
According to the preferred embodiment of FIGS. 7A and 7B, substrate
42 is "folded" three times, about three respective axes. For
example, substrate 42 may be folded, first, about a 45 degree axis
170, then, about an axis 172 parallel to the advance of substrate
42 and, finally, about another 45 degree axis 174. It should be
appreciated that such triple "folding" of substrate 42 by inverter
130 results in an inverted substrate 42 whose direction of motion
is generally parallel to the original direction but has second
surface 103 as its top surface. Folding at the above specified axes
is preferably performed by providing elongated rollers 171, 173 and
175, having preselected diameters, along axes 170, 172 and 174,
respectively. To prevent damage to substrate 42, rollers 171, 173
and 175 are preferably appropriately separated, as shown
schematically in FIG. 7B, such that substrate 42 is folded by less
then 180 degrees at each axis.
It should be appreciated that other configurations of inverter 130
may be equally suitable for inverting the surfaces of substrate 42
as described above, for example a Mobius belt arrangement wherein
the substrate is inverted by being gradually rotated about its
longitudinal axis while being advanced. However, the arrangement of
FIGS. 7A and 7B has been found to be effective in operation and
economic in space.
Downstream of inverter mechanism 130, web 42 is directed around a
support roller 126 towards impression roller 41, passing a second
detector 128 which is operative for detecting the post-image
synchronization marks imprinted between the images on surface 101.
Impression roller 41 is driven by a second impression motor 162,
which is activated by controller 150 in accordance with the
predetermined imaging sequence. In accordance with a preferred
embodiment, impression roller 41 is urged against the surface of
ITM 40 only when second surface 103 of web 42 is to be imaged
according to the imaging sequence. In a preferred embodiment, each
period of engagement between surface 103 with ITM 40, i.e. each
second surface imaging cycle, is initiated by a Second Image
Trigger signal from controller 150.
According to a preferred embodiment of the invention, before each
second surface imaging cycle, web 42 is accelerated by motor 162
and by a second indexing motor 164 which is described below, until
the velocity of surface 103 is comparable with the surface velocity
of ITM 40. This allows position controlled, slip-free, engagement
between surface 103 and ITM 40 during imaging on the second
surface.
In a preferred embodiment, web 42 is rewound, preferably by reverse
operation of motors 160, 162 and 164, after each second surface
imaging cycle. This provides the length of web necessary for
subsequent reacceleration of web 42 for the next second surface
imaging cycle. Correct positioning of a given second surface image
is enabled by detection of the post-image mark of the preceding
first surface image, so as to accurately position the given second
surface image opposite its corresponding image on surface 101.
To prevent false detection of the post-image marks, detector 128 is
preferably operative only within preset detection time windows,
during which time controller 150 queries for a detection signal
therefrom. The time gaps between consecutive detection time windows
are preferably the same as those of the respective first surface
images. These time gaps are preferably calculated by controller 150
based on the substrate length of the corresponding images, as
measured by the encoders associated with indexer rollers 116 and
117.
It is appreciated that in order to maintain the minimal spacing
between images, as described above, the page layout of each image
on surface 103 is preferably the same as that of the corresponding
image on surface 101. The second surface images are preferably
bottom-justified on ITM 40, as described above regarding the first
surface images.
Web 42, which now bears a series of images on first surface 101 and
a corresponding series of images on opposite surface 103, is guided
by a roller 132 and then passes through a second indexing rollers
134 and 135 which are preferably driven by second indexing motor
164. Indexing motor 164 communicates with controller 150 and is
operative together with motor 160, to advance web 42 in accordance
with the second surface imaging cycles, i.e. for a specified length
of web 42 after each Second Image Trigger signal generated by
controller 150. The velocity and relative position of web 42 during
each second surface imaging cycle are preferably monitored by
controller 150 through an encoder which is preferably associated
with rollers 134 and 135.
Downstream of indexing rollers 134 and 135, continuous web 42 is
guided into a third free-loop arrangement 137, having maximum
height detectors 136 and minimum height detectors 138 associated
with controller 150. Detectors 136 are activated when the loop of
substrate 42 dispensed into arrangement 137 is above a
predetermined maximum height, while detectors 138 are activated
when the loop of substrate 42 in arrangement 137 is below a
predetermined minimum height. When detectors 138 are activated,
controller 150 activates an output motor 166 which drives output
rollers 142 and 143, downstream of a support roller 140, to collect
web 42 from loop arrangement 137 thereby to raise the loop in
arrangement 137. When detectors 136 are activated, controller 150
deactivates motor 166 so as to stop output rollers 142 and 143 from
collecting web 42 from loop arrangement 137, thereby to deepen the
loop in arrangement 137. In this manner, the length of substrate 42
in loop arrangement 137 is maintained within a predetermined length
range which allows sufficient imaging timing flexibility.
The double-sided image bearing substrate 42 exiting output rollers
142 and 143 is then cut between images by a cutter 146, as known in
the art. To enable cutting of substrate 42 precisely at the spaces
between consecutive double-sided images, a third detector 144 is
provided between rollers 142 and 143 and cutter 146 for detecting
the post-image marks imprinted between the images on surface 101.
The position of substrate 42 relative to cutter 146 is adjusted by
controlled operation of output motor 146 based on the detection
signals from third detector 144 to controller 150.
To prevent false detection of the post-image marks, detector 144 is
preferably operative only within preset detection time windows,
during which time controller 150 queries for a detection signal
therefrom. The time gaps between consecutive detection time windows
are preferably the same as those of the respective first and second
surface images. These time gaps are preferably calculated by
controller 150 based on the substrate length of the corresponding
images, as measured by the encoders associated with indexer rollers
134 and 135.
In the preferred embodiment described above, eight motors are
involved in the operation of the web-feeder system, namely, motors
152, 154, 156, 158, 160, 162, 164 and 166. According to a preferred
embodiment of the invention, motors 152-164 are brushless
servo-motors driven by a plurality of corresponding digital
servo-drivers (not shown), as known in the art.
The predetermined imaging sequence, according to which controller
150 controls the operation of web-feeder system 100, may be as
follows. First, a predetermined number of images are reproduced on
first surface 101 to account for the length of continuous substrate
42 separating between first impression roller 39 and second
impression roller 41. Then, ITM 40 is alternatingly engaged by
surfaces 101 and 103 such that each first surface imaging cycle is
followed by a second surface imaging cycle.
It should be noted that, inherently, there is a considerable time
gap between imaging of a given image on surface 101 and imaging of
the corresponding image on surface 103, due to the length of
continuous substrate 42 between region 239 and region 241.
Similarly, there is an inherent time gap between imaging of the
second surface images and cutting of substrate 42 by cutter 146,
due to the length of continuous substrate 42 between region 241 and
cutter 146. It should be further noted that the length of substrate
42 between impression region 239 and impression region 241 varies
in accordance with the length of substrate 42 reserved in loop
arrangement 119. Similarly, the length of substrate 42 between
impression region 241 and cutter 146 varies in accordance with the
length of substrate 42 reserved in loop arrangement 137. Therefore,
the present invention provides an initiation procedure for
synchronizing between the first surface imaging cycles, the second
surface imaging cycles and the cutting of substrate 42.
According to the initiation procedure of the present invention,
imaging begins with substrate 42 being at a "stretched-out"
configuration, wherein substrate 42 is stretched across loop
arrangements 119 and 137, i.e. extends directly from indexers 116
and 117 to roller 122 and from indexers 134 and 135 to roller 140.
It should be appreciated that in this configuration, the length of
substrate 42 between impression regions 239 and 241 and the length
of substrate 42 between region 241 and cutter 146 are both well
defined.
A plurality of first surface images are then produced on surface
101, as described above, and controller 150 keeps track of the
length of substrate 42 passing through impression region 239, for
example by measuring the length of substrate passing through
indexer rollers 116 and 117. This length may be added to the known
length of the stretched substrate between regions 239 and 241. The
advance of substrate 42 through region 239 results in deepening of
the loop of substrate in loop arrangement 119, until minimum height
detectors 120 are activated as described above. At this stage,
substrate 42 starts to advance also through impression region 241,
and the length of this advance is monitored by controller 150 using
indexer rollers 134 and 135. The length of substrate 42 between
regions 239 and 241 is monitored by controller 150 by subtracting
the length measured at indexers 134 and 135 from the length
measured at indexer 116 and 117. Based on this information,
controller 150 synchronizes between the detection time windows of
the first surface imaging cycles and the corresponding detection
windows of the second surface imaging cycles.
The advance of substrate 42 through region 241 results in deepening
of the loop of substrate in loop arrangement 137, until minimum
height detectors 138 are activated as described above. At this
stage, substrate 42 starts to advance also through cutter 146. The
length of substrate 42 between region 241 and cutter 146 is readily
monitored by controller 150 by adding the length measured at
indexers 134 and 135 to the initial length of substrate stretched
between region 241 and cutter 146. Based on this information,
controller 150 synchronizes between the detection time windows of
the imaging cycles and the corresponding detection windows which
are used for timing the cutting at cutter 146.
It will be appreciated by persons skilled in the art that the
present invention is not limited to what has been particularly
shown and described hereinabove. Rather, the scope of the present
invention is defined only by the claims that follow:
* * * * *